According to institution of electrical and electronics engineers (IEEE) 802.16m standard published in July 2009, an uplink hybrid automatic repeat request (UL HARQ) scheme is used to detect and correct errors in data transmitted from a base station to a mobile station. The mobile station may detect if an error is included in the received data. If no error is detected, the mobile station may send an acknowledgement (ACK) signal to the base station. Otherwise, the mobile station may send a non-acknowledgement (NACK) signal to the base station, so that the base station may be informed that the data is unsuccessfully received and may retransmit the data to the mobile station.
Therefore, the ACK/NACK signal is important to ensure communication reliability. Usually, a dedicated channel resource may be allocated to transmit the ACK/NACK signal.